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The Worthington Pump.

73*

one suction valve to each end of the cylinder,* and the plunger
becomes a piston.

All the preceding may be driven by steam power. The oldest
steam pump yet in use is the Cornish engine A, Fig. 726. Its
pumps are of the lift type, arranged in relays with less than 30 ft.
between each pair, and the water is lifted from tank to tank till it
reaches the surface. Two forms of f donkey pump ' are also
shewn at 4, Fig. 447, and i, Fig. 448, pp. 486 and 488, where the
engine valves are operated from a crank shaft There is, how-
ever, another class of pump which dispenses with the crank, being
therefore called ' direct-acting,' and probably the best of this class
are those that necessarily work in pairs, being termed * duplex.'

The Worthington Pump is a duplex steam pump, its ordinary
form being shewn in Figs. 720 and 7200. Two steam cylinders
side by side at A, have pistons connected directly to two pump
plungers at B. When a D valve is employed for an engine
working without expansion, the valve and piston strokes cross
mutually at half phase, and the piston cannot then directly
actuate the valve. In this pump, piston No. i works valve No. 2,
and piston No. 2 moves valve No. i, by lever gear, the motion of
the two pistons being alternate; thus, levers L and M rock valve-
levers / and m respectively. The valves and pistons are, however,
so interdependent, that immediately steam enters either cylinder,
the action of the engine commences as a whole, and will continue
unless special friction difficulties intervene. To enable each
piston stroke to be completed before the valve reopens to steam,
the exhaust ports c c are separate from the steam ports D D ;
a quantity of steam is thus also imprisoned as a cushion. In the
pump, E EX are the suction, and F FX the respective delivery valves,
small and numerous, to give sufficient area while diminishing the
closing blow. The arrangement, also, enables the pump to both
draw and deliver at every stroke, and the contrivance is double-
acting ; in addition, the air vessel j equalises the flow, and the
water leaves at K.

The expansive use of steam has been provided for in the
Worthington high-duty engine, Fig. 721.    The engines are a pair
of tandem-compounds, where A is the high-pressure, and B the
* Except in the case of the accumulator pump, Fig. 722,

3 c